Washing maching appliance with a drain pump

ABSTRACT

A washing machine appliance is provided. The washing machine appliance includes a wash basket rotatably mounted within a wash tub and a drain pump for removing liquid from the wash tub. During a spin cycle of the washing machine appliance, the drain pump may be activated during an acceleration portion of the spin cycle. Further, the drain pump may be operated at a first duty cycle for a first portion of a dwell step of the spin cycle and at a second duty cycle for a second portion of the dwell step of the spin cycle.

FIELD OF THE INVENTION

The present subject matter relates generally to washing machine appliances and methods for operating the same.

BACKGROUND OF THE INVENTION

A washing machine appliance generally includes a cabinet with a wash tub mounted therein. The wash tub includes a sump that collects liquid disposed within wash tub. A wash basket is rotatably mounted within the wash tub and can receive articles for washing. The washing machine appliance also includes a drain pump that is in fluid communication with the sump of the wash tub. The drain pump can selectively direct a flow of liquid out of the sump, e.g., in order to drain the sump of liquid.

During a wash cycle of the washing machine appliance, wash liquid, e.g., detergent, fabric softener, bleach, and/or water, can fill the wash tub and be applied to articles within the wash basket. Such wash liquid can assist with cleaning of the articles, e.g., as the articles are agitated during the wash cycle. After the wash cycle, the washing machine appliance can rinse the wash fluid from the articles, e.g., using fresh water. After the rinse cycle, the washing machine appliance can initiate one or more spin cycles to remove liquids from the articles. During the spin cycles, the wash basket can be rotated at relatively high speeds to wring liquid from the articles. Such liquid can flow out of the articles and collect within the sump of the wash tub. In turn, the drain pump can be utilized to remove the liquid from the wash tub.

Presently, during the spin cycle, the drain pump is activated continuously or for a predetermined time interval in order to insure that liquid does not overflow the sump and negatively affect washing machine performance. For example, if liquid overflows the sump, such liquid can impact a bottom of the wash basket and hinder rotation of the wash basket. Similarly, the liquid can generate foam during rotation of wash basket, and such foam can increase drag on the wash basket. However, despite the potential negative effects of permitting liquid to fill the wash tub's sump, running the drain pump continuously or for a predetermined time interval during the spin cycle is often unduly conservative. In particular, an extraction rate of liquid from the articles with the wash basket (e.g., due to rotation of the wash basket) is generally much less than a drain rate of the drain pump. Thus, operating the drain pump in the manner described above is unnecessary to insure that liquid does not overflow the sump.

Further, operating the drain pump in the manner described above can lead to unnecessary wear and tear on the drain pump. In addition, operating the drain pump in such a manner can lead to overheating of the drain pump due to a concentration of thermal energy within the drain pump. Thus, the drain pump can require a thermally suitable material for construction, e.g., copper rather than a potentially cheaper though less thermally suitable material such as aluminum.

Accordingly, a method for operating a washing machine appliance such that a drain pump removes liquid from a sump of the appliance in a more efficient manner would be useful. In particular, a method for operating a washing machine appliance such that a drain rate of the washing machine appliance is about equal to an extraction rate of the washing machine appliance would be useful. Also, a method for operating a washing machine appliance such that potential overheating of the drain pump is reduced would be useful.

BRIEF DESCRIPTION OF THE INVENTION

The present subject matter provides a washing machine appliance with a wash basket rotatably mounted within a wash tub and a drain pump for removing liquid from the wash tub. During a spin cycle of the washing machine appliance, the drain pump may be activated during an acceleration portion of the spin cycle. Further, the drain pump may be operated at a first duty cycle for a first portion of a dwell step of the spin cycle and at a second duty cycle for a second portion of the dwell step of the spin cycle. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In a first exemplary embodiment, a method for operating a washing machine appliance is provided. The washing machine appliance has a cabinet with a wash tub mounted therein. The washing machine appliance also has a wash basket positioned within the wash tub. The wash basket is configured for receipt of articles for washing and is mounted for rotation relative to the cabinet. The method includes initiating a spin cycle of the washing machine appliance. The spin cycle includes an acceleration step in which the wash basket accelerates from a first angular velocity to a second angular velocity. The first angular velocity is different than the second angular velocity. The acceleration step of the spin cycle is performed during an acceleration step time interval. The spin cycle also includes a dwell step in which the wash basket rotates at about the second angular velocity. The dwell step of the spin cycle is performed during a dwell step time interval. The dwell step time interval includes a first portion and a second portion. The method further includes: running the drain pump of the washing machine appliance during the acceleration step of the spin cycle for about the acceleration step time interval; operating the drain pump of the washing machine appliance at a first duty cycle during the dwell step of the spin cycle for about the first portion of the dwell step time interval; and working the drain pump of the washing machine appliance at a second duty cycle during the dwell step of the spin cycle for about the second portion of the dwell step time interval.

In a second exemplary embodiment, a washing machine appliance is provided. The washing machine appliance includes a cabinet and a wash tub mounted within the cabinet. The wash tub is configured for holding liquid during operation of the washing machine appliance. A wash basket is rotatably mounted within the wash tub. The wash basket is configured for receipt of articles for washing. A motor is in mechanical communication with the wash basket such that the motor selectively rotates the wash basket. A drain pump is in fluid communication with the wash tub. The drain pump is configured for selectively urging liquid out of the wash tub. The washing machine appliance also includes a processing device in communication with the drain pump and the motor. The processing device is configured for initiating the motor during a spin cycle of the washing machine appliance. The spin cycle includes an acceleration step in which the motor accelerates the wash basket from a first angular velocity to a second angular velocity. The first angular velocity is different than the second angular velocity. The acceleration step of the spin cycle is performed during an acceleration step time interval. The spin cycle also includes a dwell step in which the motor rotates the wash basket at about the second angular velocity. The dwell step of the spin cycle is performed during a dwell step time interval. The dwell step time interval has a first portion and a second portion. The processing device is further configured for: running the drain pump during the acceleration step of the spin cycle for about the acceleration step time interval; operating the drain pump at a first duty cycle during the dwell step of the spin cycle for about the first portion of the dwell step time interval; and working the drain pump at a second duty cycle during the dwell step of the spin cycle for about the second portion of the dwell step time interval.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 provides a perspective view of a washing machine appliance according to an exemplary embodiment of the present subject matter. A portion of a cabinet of the washing machine appliance has been removed to reveal certain interior components of the washing machine appliance.

FIG. 2 is a partial, section view of the washing machine appliance of FIG. 1.

FIG. 3 illustrates plots of rotational speed of a wash basket of a washing machine appliance in rotations per minute versus time in seconds and weight of the wash basket in pounds versus time in seconds during a spin cycle of the washing machine appliance.

FIG. 4 illustrates a method for operating a washing machine appliance according to an exemplary embodiment of the present subject matter.

FIG. 5 illustrates another method for operating a washing machine appliance according to an additional exemplary embodiment of the present subject matter.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 is a perspective view partially broken away of a vertical axis washing machine appliance 50 according to an exemplary embodiment of the present subject matter. While discussed in the context of washing machine appliance 50, using the teachings disclosed herein, it should be understood that washing machine appliance 50 is provided by way of example only. Other washing machine appliances having different appearances and different features may also be utilized with the present subject matter as well, e.g., horizontal axis washing machine appliances.

Washing machine appliance 50 includes a cabinet 52 and a cover 54. A backsplash 56 extends from cover 54, and a control panel 58 including a plurality of input selectors 60 is coupled to backsplash 56. Control panel 58 and input selectors 60 collectively form a user interface input for operator selection of washing machine cycles and features, and in one embodiment, a display 61 indicates selected features, a countdown timer, and/or other items of interest to machine users. A lid 62 is mounted to cover 54 and is rotatable about a hinge (not shown) between an open position (not shown) facilitating access to a wash tub 64 located within cabinet 52, and a closed position (shown in FIG. 1) forming an enclosure over wash tub 64.

Wash tub 64 includes a bottom wall 66 and a sidewall 68, and a wash basket 70 that is rotatably mounted within wash tub 64. A drain pump or pump assembly 72 is located beneath tub 64 and wash basket 70 for gravity assisted flow when draining tub 64. Pump assembly 72 includes a pump 74 and a motor 76. A pump inlet hose 80 extends from a wash tub outlet 82 in tub bottom wall 66 to a pump inlet 84, and a pump outlet hose 86 extends from a pump outlet 88 to an outlet 90 and ultimately to a building plumbing system discharge line (not shown, e.g., a sewer or septic line) in fluid communication with outlet 90.

FIG. 2 is a front sectional view of washing machine appliance 50 including wash basket 70 movably disposed and rotatably mounted in wash tub 64 in a spaced apart relationship from tub sidewall 68 and the tub bottom 66. Wash basket 70 includes an opening for receiving wash fluid and articles for washing, e.g., clothing, bedding, etc., therein. Wash basket 70 defines a plurality of perforations 71 to facilitate fluid communication between an interior of wash basket 70 and wash tub 64.

An agitation element 92, such as a vane agitator, impeller, auger, or oscillatory basket mechanism, or some combination thereof is disposed in wash basket 70 to impart an oscillatory motion to articles and liquid in wash basket 70. In different embodiments, agitation element 92 includes a single action element (i.e., oscillatory only), double action (oscillatory movement at one end, single direction rotation at the other end) or triple action (oscillatory movement plus single direction rotation at one end, singe direction rotation at the other end). As illustrated in FIG. 2, agitation element 92 is oriented to rotate about a vertical axis A. Wash basket 70 and agitator 92 are driven by pancake motor 94. As motor output shaft 98 is rotated, wash basket 70 and agitation element 92 are operated for rotatable movement within wash tub 64.

Washing machine appliance 50 may also include a brake assembly (not shown) selectively applied or released for respectively maintaining wash basket 70 in a stationary position within wash tub 64 or for allowing wash basket 70 to spin within wash tub 64. Pump assembly 72 is selectively activated, e.g., to remove liquid from wash basket 70 and wash tub 64 through drain outlet 90 during appropriate points in washing cycles as washing machine appliance 50 is used.

Operation of washing machine appliance 50 is controlled by a controller or processing device 63 (FIG. 1) that is operatively coupled to the user interface input located on backsplash 56 for user manipulation to select washing machine cycles and features. In response to user manipulation of the user interface input, controller 63 operates the various components of washing machine appliance 50 to execute selected machine cycles and features as described in greater detail below.

Controller 63 may include a memory and microprocessor, such as a general or special purpose microprocessor operable to execute programming instructions or micro-control code. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In one exemplary embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor.

Controller 63 may be positioned in a variety of locations throughout washing machine appliance 50. In the illustrated exemplary embodiment, controller 63 is located within backsplash 56 as shown. In such an embodiment, input/output (“I/O”) signals may be routed between controller 63 and various operational components of washing machine appliance 50, e.g., pump assembly 72 and/or pancake motor 94, along wiring harnesses (not shown). Controller 63 is also operatively coupled to control panel 58 and input selectors 60 through which a user may select various operational features and modes and monitor progress of washing machine appliance 50. In one exemplary embodiment, input selectors 60 may represent a general purpose I/O (“GPIO”) device or functional block. Control panel 58 and input selectors 60 may be in communication with controller 63 via one or more signal lines or shared communication busses.

As an example, laundry items can be loaded into wash basket 70, and washing operation can be initiated through operator manipulation of control input selectors 60. Wash tub 64 is filled with water and mixed with detergent to form a wash fluid, and contents of the wash basket 70 are agitated with agitation element 92 for cleansing of laundry items in wash basket 70. More specifically, agitation element 92 is moved back and forth in an oscillatory back and forth motion.

After the agitation phase of the wash cycle is completed, wash tub 64 is drained with pump assembly 72. Laundry items are then rinsed and portions of the cycle repeated, including the agitation phase, depending on the particulars of the wash cycle selected by a user. One or more spin cycles may also be performed. In particular, a spin cycle may be applied after the wash cycle and/or after the rinse cycle in order to wring wash fluid from the articles being washed. During a spin cycle, wash basket 70 is rotated at relatively high speeds by pancake motor 94 such that wash fluid exits the wash basket 70 at an extraction rate. As wash fluid exits wash basket 70, e.g., through plurality of perforations 71, such wash fluid enters wash tub 64 where pump assembly 72 is utilized to remove such wash fluid from washing machine appliance 50 at a drain rate.

As will be understood by those skilled in the art, the extraction rate of wash fluid exiting the wash basket 70 during the spin cycle is a function of many variables. For example, the extraction rate can vary as a function of the volume of wash fluid contained within articles in wash basket 70 and the angular velocity of the wash basket 70. Similarly, the drain rate of pump assembly 72 is also a function of many variables. For example, the drain rate can vary as a function of pump assembly design, customer drain height, and any degradation of the building plumbing system discharge line over time. In order for washing machine appliance 50 to operate more efficiently, the drain rate of pump assembly 72 can be matched to the extraction rate of washing machine appliance 50 during spin cycle, e.g., utilizing the methods described below.

FIG. 3 illustrates plots of rotational speed of wash basket 70 in rotations per minute versus time in seconds and weight of wash basket 70 in pounds versus time in seconds during an exemplary spin cycle of the washing machine appliance 50. Such spin cycle may be performed after a wash cycle of washing machine appliance 50 and/or after a rinse cycle of washing machine appliance 50 in order to wring liquid from articles disposed within wash basket 70. The spin cycle shown in FIG. 3 is provided by way of example only and is not intended to limit the present subject matter in any regard. Thus, washing machine appliance 50 may operate with alternative exemplary spin cycles with similar or different characteristics from the exemplary spin cycle shown in FIG. 3.

As may be seen in FIG. 3, the exemplary spin cycle has four distinct portions: a low speed (LS) portion; a moderate speed (MS) portion; a high speed (HS) portion; and a brake portion. During the low speed portion of the spin cycle, the wash basket 70 first accelerates from about zero rotations per minute to about one-hundred and fifty rotations per minute during a low speed acceleration step, shown as A_(ls) in FIG. 3. The wash basket 70 rotates at about one-hundred and fifty rotations per minute during a low speed dwell step that includes a first portion and a second portion, shown as D_(ls,1) and D_(ls,2) in FIG. 3.

During the low speed portion of the spin cycle, wash basket 70 rotates at a relatively slow speed, e.g., to evenly distribute articles within the wash basket 70 and/or to permit wash fluid to exit wash basket 70 prior to rotating wash basket 70 at a greater velocity as will be understood by those skilled in the art. During, the low speed dwell step the wash basket 70 may be rotated by pancake motor 94 at any suitable angular velocity, e.g., between about ten radians per second and about twenty radians per second.

The low speed portion of the spin cycle is performed during a low speed time interval. In FIG. 3, the low speed time interval is about three minutes. However, low speed time interval may be any other suitable time interval in alternative exemplary embodiments.

During the moderate speed portion of the spin cycle, the wash basket 70 accelerates from about one-hundred and fifty rotations per minute rotations per minute to about four hundred rotations per minute during a moderate speed acceleration step, shown as A_(ms) in FIG. 3. The wash basket 70 rotates at about four hundred rotations per minute during a moderate speed dwell step that includes a first portion and a second portion, shown as D_(ms,1) and D_(ms,2) in FIG. 3.

During the moderate speed portion of the spin cycle, wash basket 70 rotates at a relatively moderate speed, e.g., to permit detection of imbalances in distribution of articles within the wash basket 70 as is well understood by those skilled in the art. During the moderate speed dwell step the wash basket 70 may be rotated by pancake motor 94 at any suitable angular velocity, e.g., between about thirty radians per second and about fifty radians per second.

The moderate speed portion of the spin cycle is performed during a moderate speed time interval. In FIG. 3, the moderate speed time interval is about one minute. However, moderate speed time interval may be any other suitable time interval in alternative exemplary embodiments.

During the high speed portion of the spin cycle, the wash basket 70 accelerates from about four hundred rotations per minute rotations per minute to about nine hundred rotations per minute during a high speed acceleration step, shown as A_(hs) in FIG. 3. The wash basket 70 rotates at about nine hundred rotations per minute during a high speed dwell step that includes a first portion and a second portion, shown as D_(hs,1) and D_(hs,2) in FIG. 3.

During the high speed portion of the spin cycle, wash basket 70 rotates at a relatively high speed compared to the lower rotational speeds described above, e.g., to extract or wring wash liquid from articles within the wash basket 70 as is well understood by those skilled in the art. During the high speed dwell step the wash basket 70 may be rotated by pancake motor 94 at any suitable angular velocity, e.g., between about eighty radians per second and about one hundred and ten radians per second.

The high speed portion of the spin cycle is performed during a high speed time interval. In FIG. 3, the high speed time interval is about five and a half minutes. However, high speed time interval may be any other suitable time interval in alternative exemplary embodiments.

During the brake portion of the spin cycle, the wash basket 70 negatively accelerates from about nine hundred rotations per minute rotations per minute to zero rotations per minute during a brake step shown as B in FIG. 3. During the brake portion of the spin cycle, rotation of wash basket 70 is stopped, e.g., to terminate the spin cycle as is well understood by those skilled in the art.

The brake portion of the spin cycle is performed during a brake time interval. In FIG. 3, the brake time interval is about half a minute. However, brake time interval may be any other suitable time interval in alternative exemplary embodiments.

As discussed above, the spin cycle shown in FIG. 3 is provided by way of example only. Thus, washing machine appliance 50 may operate with an alternative exemplary spin cycle that includes any suitable combination of the low speed portion, the moderate speed portion, and the high speed portion and may also include additional portions not shown in FIG. 3.

As may be seen in FIG. 3, the weight of wash basket 70 decreases continuously during the spin cycle. However, the weight of wash basket 70 decreases at a higher rate during the acceleration portions A_(ls), A_(ms), and A_(hs) of the spin cycle relative to the dwell steps D_(ls,1), D_(ls,2), D_(ms,1), D_(ms,2), D_(hs,1), and D_(hs,2) of the spin cycle. Similarly, the weight of wash basket 70 decreases at a higher rate during the first portion of the dwell step D_(ls,1), D_(ms,1), and D_(hs,1) relative to the second portion of the dwell step D_(ls,2), D_(ms,2), and D_(hs,2).

As will be understood by those skilled in the art, wash basket 70 decreases in weight during the spin cycle as wash liquid is extracted from articles within wash basket 70 and such wash fluid exits wash basket 70. Thus, a higher rate of weight change for wash basket 70 can correlate to an increased extraction rate for wash fluid exiting wash basket 70. Conversely, a lower rate of weight change for wash basket 70 can correlate to a decreased extraction rate for wash fluid exiting wash basket 70. As may be seen in FIG. 3, the extraction rate is greatest during the acceleration portions A_(ls), A_(ms), and A_(hs) of the spin cycle and smallest during the second portion of the dwell step D_(ls,2), D_(ms,2), and D_(hs,2).

As discussed above, wash fluid collects in wash tab 64 upon exiting the wash basket 70, and pump assembly 72 can be utilized to remove such wash fluid from washing machine appliance 50. However, pump assembly 72 generally has a drain rate that is greater than the extraction rate when pump assembly 72 is operated continuously. Thus, operating pump assembly 72 continuously during the spin cycle can be inefficient. As discussed above, the drain rate of pump assembly 72 can be matched to the extraction rate of washing machine appliance 50 during a spin cycle utilizing the methods described below.

FIG. 4 illustrates a method 400 for operating washing machine appliance 50 according to an exemplary embodiment of the present subject matter. Utilizing method 400, washing machine appliance 50 may operate more efficiently. For example, operation of pump assembly 72 may be optimized so that pump assembly 72 does not run unnecessarily. Method 400 may be implemented or carried out by controller 63.

At step 410, controller 63 initiates a spin cycle of washing machine appliance 50, e.g., the spin cycle descried in FIG. 3. The spin cycle includes an acceleration step (e.g., A_(ls), A_(ms), or A_(hs)) in which wash basket 70 accelerates from a first angular velocity (e.g., about zero radians per second) to a second angular velocity (e.g., about fifteen radians per second). The first angular velocity is different than the second angular velocity. The acceleration step of the spin cycle is performed during an acceleration step time interval. The spin cycle also includes a dwell step in which the wash basket 70 rotates at about the second angular velocity. The acceleration step and the dwell step of the spin cycle may be substantially sequential. The dwell step of the spin cycle is performed during a dwell step time interval. The dwell step time interval includes a first portion (e.g., D_(ls,1), D_(ms,1), or D_(hs,1)) and a second portion (e.g., D_(ls,2), D_(ms,2), or D_(hs,2)).

At step 420, controller 63 runs pump assembly 72 of washing machine appliance 50 during the acceleration step of the spin cycle for about the acceleration step time interval. As described above, the extraction rate for wash liquid from wash basket 70 can be greatest during the acceleration step of the spin cycle. Thus, running pump assembly 72 during the acceleration step can insure that pump assembly 72 is removing wash liquid from wash tub 64 when the extraction rate is greatest.

At step 430, controller 63 operates pump assembly 72 at a first duty cycle during the dwell step of the spin cycle for about the first portion of the dwell step time interval. Conversely, at step 440, controller 63 works pump assembly 72 at a second duty cycle during the dwell step of the spin cycle for about the second portion of the dwell step time interval. The first and second duty cycles can be different. Thus, pump assembly 72 can operate at two distinct duty cycles during the dwell step of the spin cycle.

The term “duty cycle” corresponds to proportion, e.g., a percentage or ratio, of time that pump assembly 72 spends in an active state relative to a total time period under consideration. As an example, a 60% duty cycle corresponds to controller 63 running pump assembly 72 for 60% of the relevant time period and deactivating pump assembly 72 for 40% of the relevant time period.

As discussed above, the extraction can be smallest during the second portion of the dwell step. Conversely, the extraction rate can be larger during the first portion of the dwell step relative to the second portion of the dwell step. Thus, the first and second duty cycles of the pump assembly 72 can be selected to match the extraction rates for wash basket 70 during both the first portion of the dwell step and the second portion of the dwell step. Thus, operation of pump assembly 72 can be regulated with controller 63 and operated at the first and second duty cycles to more closely match the drain rate of pump assembly 72 to the extraction rate of wash basket 70.

In additional exemplary embodiments, the spin cycle may further include an additional acceleration step in which wash basket 70 accelerates from about the second angular velocity to about a third angular velocity (e.g., about ninety-five radians per second). The third angular velocity is different than the second angular velocity. The additional acceleration step of the spin cycle is performed during an additional acceleration step time interval. The spin cycle may also further include an additional dwell step in which wash basket 70 rotates at about the third angular velocity. The additional dwell step of the spin cycle is performed during an additional dwell step time interval. The additional dwell step time interval having a first portion and a second portion.

In such embodiments, method 400 may further include the steps of: (1) running pump assembly 72 during the additional acceleration step of the spin cycle for about the additional acceleration step time interval; (2) operating pump assembly 72 at a third duty cycle during the additional dwell step of the spin cycle for about the first portion of the additional dwell step time interval; (3) and working pump assembly 72 at a fourth duty cycle during the additional dwell step of the spin cycle for about the second portion of the additional dwell step time interval. The third duty cycle may be greater than the fourth duty cycle. The acceleration step, the dwell step, the additional acceleration step, and the additional dwell step of the spin cycle may be substantially sequential. In addition, the first duty cycle may be equal to or different from the third duty cycle. Similarly, the second duty cycle may be equal to or different form the fourth duty cycle.

In a further exemplary embodiment, the spin cycle further includes a brake step in which the wash basket 70 accelerates negatively from about the second angular velocity to about a zero angular velocity. The zero angular velocity is different than the second angular velocity. The method 400 may further include the step of utilizing pump assembly 72 during the brake step of the spin cycle for a predetermined period of time. The predetermined period of time may be any suitable period of time, e.g., about thirty seconds.

FIG. 5 illustrates a method 500 for operating washing machine appliance 50 according to an additional exemplary embodiment of the present subject matter. Utilizing method 500, washing machine appliance 50 may operate more efficiently. For example, operation of pump assembly 72 may be optimized so that pump assembly 72 does not run unnecessarily during a spin cycle. Method 500 may be implemented or carried out by controller 63.

At step 510, a spin cycle of washing machine appliance 50 is initiated, e.g., by controller 63. At steps 520, 540, and 550, controller 63 determines a stage of the spin cycle in which the washing machine appliance 50 is operating. In particular, at step 520, controller 63 determines whether the spin cycle is in an acceleration step. Similarly, at step 540, controller 63 determines whether the spin cycle is in a dwell step. Also, at step 550, controller 63 determines whether the spin cycle is in a brake step.

If controller 63 determines that the spin cycle is in the acceleration step at step 520, controller 63 runs pump assembly 72. Conversely, if controller 63 determines that the spin cycle is in the dwell step at step 540, controller 63 then determines if the spin cycle is in a first portion at step 542. If controller 63 determines that the spin cycle is in the first portion, controller 63 operates pump assembly 72 at a first duty cycle. Conversely, if controller 63 determines that the spin cycle is in not the first portion, controller 63 operates pump assembly 72 at a second duty cycle. At step 550, if controller 63 determines that the spin cycle is in the brake step, controller 63 operates pump assembly 72 for a predetermined time interval. At 530, controller 63 determines whether the spin cycle is complete.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A method for operating a washing machine appliance, the washing machine appliance having a cabinet with a wash tub mounted therein, the washing machine appliance also having a wash basket positioned within the wash tub, the wash basket configured for receipt of articles for washing and mounted for rotation relative to the cabinet, the method comprising: initiating a spin cycle of the washing machine appliance, the spin cycle comprising: an acceleration step in which the wash basket accelerates from a first angular velocity to a second angular velocity, the first angular velocity being different than the second angular velocity, the acceleration step of the spin cycle performed during an acceleration step time interval; a dwell step in which the wash basket rotates at about the second angular velocity, the dwell step of the spin cycle performed during a dwell step time interval, the dwell step time interval comprising a first portion and a second portion; running the drain pump of the washing machine appliance during the acceleration step of the spin cycle for about the acceleration step time interval; operating the drain pump of the washing machine appliance at a first duty cycle during the dwell step of the spin cycle for about the first portion of the dwell step time interval; and working the drain pump of the washing machine appliance at a second duty cycle during the dwell step of the spin cycle for about the second portion of the dwell step time interval.
 2. The method of claim 1, wherein the acceleration step and the dwell step of the spin cycle are substantially sequential.
 3. The method of claim 1, wherein the first duty cycle is greater than the second duty cycle.
 4. The method of claim 1, wherein the spin cycle of the washing machine appliance further comprises an additional acceleration step in which the wash basket accelerates from about the second angular velocity to a third angular velocity, the third angular velocity being different than the second angular velocity, the additional acceleration step of the spin cycle performed during an additional acceleration step time interval, and wherein the spin cycle of the washing machine appliance also further comprises an additional dwell step in which the wash basket rotates at about the third angular velocity, the additional dwell step of the spin cycle performed during an additional dwell step time interval, the additional dwell step time interval having a first portion and a second portion, the method further comprising the steps of: running the drain pump of the washing machine appliance during the additional acceleration step of the spin cycle for about the additional acceleration step time interval; operating the drain pump of the washing machine appliance at a third duty cycle during the additional dwell step of the spin cycle for about the first portion of the additional dwell step time interval; and working the drain pump of the washing machine appliance at a fourth duty cycle during the additional dwell step of the spin cycle for about the second portion of the additional dwell step time interval.
 5. The method of claim 4, wherein the acceleration step, the dwell step, the additional acceleration step, and the additional dwell step of the spin cycle are substantially sequential.
 6. The method of claim 4, wherein the first duty cycle and the third duty cycle are about equal, and the second duty cycle and the fourth duty cycle are about equal.
 7. The method of claim 4, wherein the third duty cycle is greater than the fourth duty cycle.
 8. The method of claim 1, wherein the spin cycle of the washing machine appliance further comprises a brake step in which the wash basket accelerates from about second angular velocity to about a zero angular velocity, the zero angular velocity being different than the second angular velocity, the method further comprising the steps of: utilizing the drain pump of the washing machine appliance during the brake step of the spin cycle for a predetermined period of time.
 9. The method of claim 8, wherein the predetermined period of time is about thirty seconds.
 10. The method of claim 1, wherein the second angular velocity is between about eighty radians per second and about one hundred and ten radians per second.
 11. A washing machine appliance comprising: a cabinet; a wash tub mounted within said cabinet, said wash tub configured for holding liquid during operation of the washing machine appliance; a wash basket rotatably mounted within said wash tub, said wash basket configured for receipt of articles for washing; a motor in mechanical communication with said wash basket such that said motor selectively rotates said wash basket; a drain pump in fluid communication with said wash tub, said drain pump configured for selectively urging liquid out of said wash tub; and a processing device in communication with said drain pump and said motor, said processing device configured for: initiating said motor during a spin cycle of the washing machine appliance, the spin cycle comprising: an acceleration step in which said motor accelerates said wash basket from a first angular velocity to a second angular velocity, the first angular velocity being different than the second angular velocity, the acceleration step of the spin cycle performed during an acceleration step time interval; a dwell step in which said motor rotates said wash basket at about the second angular velocity, the dwell step of the spin cycle performed during a dwell step time interval, the dwell step time interval having a first portion and a second portion; running said drain pump during the acceleration step of the spin cycle for about the acceleration step time interval; operating said drain pump at a first duty cycle during the dwell step of the spin cycle for about the first portion of the dwell step time interval; and working said drain pump at a second duty cycle during the dwell step of the spin cycle for about the second portion of the dwell step time interval.
 12. The washing machine appliance of claim 11, wherein the acceleration step and the dwell step of the spin cycle are substantially sequential.
 13. The washing machine appliance of claim 11, wherein the first duty cycle is greater than the second duty cycle.
 14. The washing machine appliance of claim 11, wherein the spin cycle of the washing machine appliance further comprises an additional acceleration step in which said motor accelerates said wash basket from about the second angular velocity to a third angular velocity, the third angular velocity being different than the second angular velocity, the additional acceleration step of the spin cycle performed during an additional acceleration step time interval, and wherein the spin cycle of the washing machine appliance also further comprises an additional dwell step in which said motor rotates said wash basket at about the third angular velocity, the additional dwell step of the spin cycle performed during an additional dwell step time interval, the additional dwell step time interval having a first portion and a second portion, said processing device further configured for: running said drain pump during the additional acceleration step of the spin cycle for about the additional acceleration step time interval; operating said drain pump at a third duty cycle during the additional dwell step of the spin cycle for about the first portion of the additional dwell step time interval; and working said drain pump at a fourth duty cycle during the additional dwell step of the spin cycle for about the second portion of the additional dwell step time interval.
 15. The washing machine appliance of claim 14, wherein the acceleration step, the dwell step, the additional acceleration step, and the additional dwell step of the spin cycle are substantially sequential.
 16. The washing machine appliance of claim 14, wherein the first duty cycle and the third duty cycle are about equal, and the second duty cycle and the fourth duty cycle are about equal.
 17. The washing machine appliance of claim 14, wherein the third duty cycle is greater than the fourth duty cycle.
 18. The washing machine appliance of claim 11, wherein the spin cycle of the washing machine appliance further comprises a brake step in which the wash basket accelerates from about the second angular velocity to about a zero angular velocity, the zero angular velocity being different than the second angular velocity, said processing device further configured for: utilizing said drain pump during the brake step of the spin cycle for a predetermined period of time.
 19. The washing machine appliance of claim 18, wherein the predetermined period of time is about thirty seconds.
 20. The washing machine appliance of claim 11, wherein the second angular velocity is between about eighty radians per second and about one hundred and ten radians per second. 